In connection with the development of proposed new low-power electronic telephone sets, preferably sets of universal, as nearly worldwide applicability as is feasible, it is desired to provide a set that automatically generates a substantially constant, relatively low-voltage speech network tip-to-ring supply voltage and a uniform, equalized speech network loop current, as described in detail in the copending application cited above, such as 6 volts .+-.1/4 volt and 20-25 ma in a typical example, regardless of the input supply voltage to the set.
In conventional American telephone networks (no active devices in the speech network), the impedance of the set is matched (by varistor networks built into the set) to that of the transmission line by drawing relatively high telephone set currents (such as 150 ma) on short loops and relatively low currents (such as 20 ma) on long loops. Such networks are inherently passive (no gain), and cannot boost transmitted signal level or increase receive sensitivity.